The present invention relates generally to dynamoelectric machines such as electric generators, and more particularly to redistributing heat from an end of a stator core assembly of an electric generator.
A typical stator core assembly of an electric generator generally includes a stack of thin, insulated, low-loss, electrical steel laminations disposed between inside space block assemblies and outside space block assemblies. Stator flanges along with key bars, which are part of the stator frame that enclose the stator core assembly, maintain a compressive load on the laminations and the space block assemblies that can withstand electromagnetic forces that are present during operation of the electric generator.
The stator core assembly along with other components form a stator. The stator, which is wrapped in armature winding, encloses a rotor wrapped with field winding. In the operation of the electric generator, a turbine such as a steam turbine or gas turbine, drives the rotor to rotate within the stator. An electromagnetic field is induced by rotating the rotor within the stator. The electromagnetic field induced by rotating the rotor induces eddy currents in the stator. The eddy currents are magnetically and electrically resistive and cause the dissipation of energy in the stator in the form of heat (i.e., hot spots). As a result, the eddy currents impose a thermal constraint on the operation of the generator. One particular area in the stator where hot spots arise is at the ends of the core stator assembly along the inner diameter of the stator flanges. Attempts to reduce hot spots at the stator flanges have included providing increased ventilation to the flanges and using flux shields disposed over the flanges to protect against the development of fluxes which induce the eddy currents. Neither approach provides an adequate solution to reducing hot spots at the stator flanges. In particular, increasing ventilation to the flanges is inadequate at reducing hot spot temperatures because this ends up increasing windage losses in the stator, and adding flux shields necessitates substantial design efforts that translate to significant costs.